The invention relates to magnet wire and more particularly to a magnet wire having a surprisingly concentric and continuous coating superimposed thereon.
Magnet wire has been conventionally manufactured by passing a bare copper or aluminum conductor or a previously insulated copper or aluminum conductor through a bath of liquid enamel (a solution of resin material in a solvent thereof) and through an over for driving off the solvent from the enamel and/or curing the resin, leaving a resin coat on the conductor.
The application of several coats of material to a filament from solution accounts for all of the magnet wire manufactured today. While some materials using today's technology can only be applied from solution, the cost of the solvent expended in applying resin materials from solution is usually significant. The machinery used in this process is also highly complex and expensive, although the machinery cost is usually not a factor since most of such machinery has been in use for a considerable number of years. Still, the original cost of such machinery is significant for new installations. In addition to the cost machinery and the solvent expended by such a process, there is the cost of providing and maintaining pllution control equipment; since recently both Federal and State laws have required that the oven stack gases of such machines by essentially stripped of solvent before exhausting the gases to the atmosphere. While various methods of burning the vaporized solvent and/or reclaimng the solvent have been proposed, all such methods result in further expense to the manufacturer.
Additionally, the application of a layer of material to a filament from solution usually requires several successive coats in order to result in a concentric coat of a desired thickness. For example, six coats may be required for a 3 mil coating, although in specific applications as many as 24 coats have been required. Also, multiple coats of certain materials, such as polyethylene terephthalate (PET) cannot be applied successfully from solution due to a lack of good adhesion and wetting between coats.
It therefore has been desirable for some time to provide an improved magnet wire which can be manufactured without the use of solvent. Also, it would be additionally highly desirable to provide an improved magnet wire which could be manufactured utilizing an apparatus of simple design. Also, it would be highly desirable to provide magnet wire manufactured by a process which would allow the wire to be drawn, coated and spooled in a continuous operation; conventinally the wire is drawn, annealed if necessary, spooled; and then coated and spooled again for shipment. Also, it would be highly desirable to provide a magnet wire which can successfully be manufactured by application of multiple layers of materials such as polyethylene terephthalate (PET), which has heretofore not been possible. Additionally, it would be highly desirable to provide a magnet wire having a coating thereon of improved continuity and concentricity. Finally, it would be highly desirable to provide an improved magnet wire, the manufacture of which would not require the use of solvent or pollution control apparatus, or be limited to materials requiring an oven cure, or require multiple coats to obtain a coating of the required continuity and concentricity.
Applying coatings of resinous material by extrusion is substantially less common that applying coatings from solution, since conventional extrusion processes are extremely limited. Coatings of 4 mils and less are either extremely difficult to apply or impossible to apply by conventional extrusion processes. Also, the number of materials which are normally applied by conventional extrusion processes are extremely limited. Polyvinylchloride, polyethylene, polypropylene and various elastomeric rubbers comprise 99% of the materials applied by extrusion. These materials are not used in a true magnet wire application, i.e. an electrical winding, the turns of which are insulated to provide low voltage, mechanical, and thermal protection between turns, and do not possess magnet wire properties. In contrast, these materials are conventionally used in lead wire or hook-up wire applications which must protect against the full imput line voltage of an electrical device. Conventinally, extrusion is used in the production of only cables, building wire, and lead or hook-up wire.
While the apparatus used in conventional extrusion processes is relatively simple when compared to a conventional wire coating tower, and the extrusion process can be carried out continuously whereby the filament may be drawn, coated and spooled in a continuous operation, still, a conventional extrusion apparatus is not without problems. Conventional extruders include a centering die, a material reservoir and a sizing die. The centering die mechanically centers the filament in the sizing die, the sizing die determines the exterior dimensions of the coated filament and the thickness of the coat applied to the filament. The primary problem associated with extrusion apparatus is the wear on the centering die. Since the centering die is used to center the filament within the sizing die, the centering die must be finely adjusted to achieve a concentric coating and must be replaced periodically due to the wear resulting from the contact between the filament and the die. Centering dies tend to be expensive even when made of hardened steel; but because of the wear that occurs, diamond centering dies have been considered, but not widely used.